Heat exchangers, especially automotive radiators, typically include a coolant tank that relies upon an elastomer gasket for a fluid tight seal. Displacement of the gasket during or after installation threatens the integrity of the seal, and the leaks caused thereby can have a dynamic aspect that makes the leak difficult to detect.
An example may be seen in the attached FIGS. 1 through 7. An open sided, molded plastic tank, indicated generally at 10, has a four sided outer wall 12 the bottom edge of which is integrally molded with a thickened perimeter foot 14. A slotted aluminum tube header plate, indicated generally at 16, is stamped with an integral, four sided, U shaped perimeter channel 18. The inner surface of the channel 18 merges into the inner surface of the header plate 16 across a curved, generally right angle bend. The outer edge of the U shaped channel 18 includes a plurality of clinch tabs 20, which are ultimately crimped down over the top of the foot 14, as seen in FIG. 3. Foot 14 is deliberately less wide than the channel 18, so as to fit within it without binding, leaving slight gaps relative to the side surfaces of the channel 18. Since the inner surface of the tank outer wall 12 diverges sharply from the inner surface of the header plate 16 (at essentially a right angle) it forms an open, divergent, perimeter crevice C running from beneath the tank foot 14 to the interior of the tank 10.
The purpose of crimping foot 14 within channel 18, besides attaching the tank 10, is to compress a continuous elastomer seal gasket 22, which is first fitted down into channel 18, as best seen in FIG. 1. When the gasket 22 is clinched beneath the foot 14, a continuous perimeter seal is created so that fluid cannot leak through the crevice C and out, as seen in FIG. 4. A not previously well recognized problem is the potential for gasket 22 to be misplaced before the clinch operation is completed, creating a potential leak path. As best seen in FIGS. 2 and 5, the gasket 22 is relatively long, and is subject to not being fully seated within channel 18, particularly at the corners, where it can ride up over the curved corner of the header plate 16-channel 18 transition. Then, as seen in FIG. 6, after the clinch operation, a portion of the gasket 22 can be squeezed and compressed within the crevice C, rather than being properly compressed down beneath the foot 14. This may not create a leak, so long as the coolant in the interior of the tank 12 is under a positive pressure, as it generally is during vehicle radiator operation. This is indicated by the arrows in FIG. 6, representative of positive pressure acting to press the displaced portion of gasket 22 back down into the crevice C. However, during the radiator coolant fill operation at the assembly plant, the radiator tanks are subjected to negative pressure, the so called vacuum fill operation. This puts the gasket 22 under a negative pressure, indicated by the reversed arrows in FIG. 7, which can pull the displaced portion thereof further, or completely, out of the crevice C, opening a potential leak path. However, the leak may disappear later, after a short period of positive pressure, and such leaks can ultimately prove very elusive and difficult to detect.
The crevice generally indicated at C has found mention in the prior art, but not in the context of gasket leak creation and detection just noted. Rather, a different problem of corrosion created by stagnant coolant resting in the crevice has been noted, and various techniques for its prevention proposed. Most often, this takes the form of integrally molded flanges added to the gasket 22, which fill up the crevice C and keep stagnant coolant out. In fact, such a flange is shown on gasket 22, and is described in coassigned U.S. Pat. No. 5,201,368, as well as a similar design disclosed in coassigned U.S. Pat. No. 5 4,917,182. However, the efficacy of such a design presupposes proper and complete gasket placement, and does nothing to deal with the elusive leak potential just noted. Another known design proposes stand off ribs molded to the rear surface of the tank foot within the U shaped channel, and apparently intended to hold the inner surface of the tank wall consistently away from the inner surface of the channel. This keeps the crevice open wide, in effect, and is claimed to somehow promote mixing of the coolant within the crevice to prevent stagnation and corrosion. The ribs disclosed are flush to the inner surface of the tank outer wall, and fit within the U shaped channel in line with the inner surface of the U shaped channel. They would do little or nothing to prevent the kind of dynamic gasket displacement and leakage noted above, and are not intended or designed to do so.